I can't think of anything recent. But the PDP-1 and some UNIVAC used ones complement. I want to say the IBM 7090 used sign-magnitude, but I'm not sure about that one. Well technically, the UNIVAC 2200 series was released until the late 90's, so you might be able to find one of those running ones complement in the real world if you look hard enough. But I don't think the JVM was ported to any of those.